Interpolyesters of bibenzoic acid



- melting point since INTERPOLYESI'ERS or BIBENZOIC ACID, AN ALl- PHATICDICARBOXYLIC ACID AND A GLYCOL Edward A. Wieliclri, Philadelphia, andRobert D. Evans,

West Chester, Pa., assignors to American Viscose Corporation,Philadelphia, Pa., a corporation of Delaware No Drawing. Filed July 28,1958, Ser. No. 751,169

5 Claims. (Cl. 260-75) This invention relates to new and usefulinterpolyesters, shaped articles prepared therefrom and methods ofpreparing the same. More particularly it is directed to uniqueinterpolyesters of bibenzoic acid, a glycol and an aliphaticdicarboxylic acid. This invention relates further to films, fibers,molded products, coatings andother shaped articles prepared from theunique interpolyesters described above.

The history of polyesters is a relatively short but active one.Condensation polyesters, while encountered in early researches such asthose of Lourenco, Bischotf, Fischer, etc., were not intensively studieduntil 1928, when Carothers and coworkers began a systematic study ofcondensation polymerization. Illustrative of Carothers work is US.Patent No. 2,071,250 (1937 which discusses some of the previous work inthe field and some of the problems in drawing polyesters into fibers.Carothers produced filaments from his polyesters, but they werelow-melting and lacked hydrolytic stability.

The current prior art describes various linear condensation polyestersderived from dihydroxy compounds and dibasic acids, such as terephthalicacid, which are capable of being drawn into fibers showing, bycharacteristic X-ray patterns, orientation along the fiber axis.However, in using a single glycol and single acid to prepare apolyester, one is limited to a fixed crystal structure and theconstitution of the polymer cannot be varied.

In recent years a limited amount of work has been done involvingbibenzoic acid and its esters in connection with homopolyesters. Theprior art indicates, however, that this work was not generally fruitful,for a homopolyester of 'bibenzoic acid and a glycol (e.g.polyethylenebibenzoate) possesses an extremely high melting point makingits use in shaped articles entirely impractical, particularly whenattempts were made to use it as a film or fiber-forming material.Moreover, and possibly more important, known polybibenzoates exhibit anextremely high rate of crystallization, making orientation of fibers orfilms therefrom extremely difficult and costly,

if not impossible, from a commercial standpoint.

This invention overcomes these limitations in providing as one of itsobjects new and useful highly polymeric interpolyesters of a glycol,bibenzoic acid and a straight or branched chain aliphatic dicarboxylicacid having valuable properties, including those of being capable ofbeing formed into useful filaments, films and the like. It is a furtherobject of this invention to provide unique interpolyesters as describedabove which possess melting points and rates of crystallization whichmake them amenable to the preparation of new and useful fibers, films,molded products, coatings, other shaped articles and the like. A stillfurther object is the provision of unique interpolyesters having a lowdegree of solubility in organic solvents. A further object is theprovision of new and useful synthetic filaments and films possessingimproved moisture regain characteristics. Another object is theprovision of new and useful synthetic fibers, film and molded objectshaving improved dyeing characteristics. A still further object is theprovision of a new process for making the unique interpolyesters of thisinvention. Other objects will appear hereinafter.

The synthetic products according to the present invention aredifiicultly soluble, usually crystallizable, orienting glycols:

2 able, highly polymerized interpolyesters of (1) bibenzoic acid, havingthe general formula:

(2) an aliphatic dibasic acid having the general formula: HOOCR,CO0H

wherein R is a bivalent straight or branched chain aliphatic hydrocarbonradical containing 2 to 10 carbon atoms, X is an ether oxygen or sulfoneand n is an integer from 1 to 6, or

wherein Ar is a monoor di-uuclear aromatic hydrocarbon radicalcontaining 6 to 12 nuclear carbon atoms and m is an integer from 1 to 4,or

wherein R, X and n are the same as in (a), Ar is the same as in (b), andp is an integer from 0 to 4, or

wherein R, X and n are the same as in (a), p is the same as in (c), andR" is thesame as in (d).

The polyesters of the present invention possess, among others, thefollowing superior fiber and film properties: (1) controlled meltingpoints over a relatively wide range, i.e. above C. and preferably2.00-270 C., (2) toughness, (3) controlled crystallizability dependentupon thermal and orienting treatment, (4) orientability, (5) pliability,and (6) lack of color. Items (1) and (3) are important in order that thefiber or film have good thermal and dimensional stability, as well asorientabil- Y, toughness, pliability and lack of color are readilyapparent. In order that these latter characteristics be attained, thefiber or film forming polymer must not crystallize too rapidly;otherwise it will not be possible to properly orient it. In other words,it must be capable of being easily converted to an amorphous form whichcan be oriented by cold or hot drawing or other known orientingprocedures. On the other hand, the fiber or film-forming polymer musthave latent ability to crystallize, for if it does not'it is thenbrittle toward impact and possesses poor dimensional stability.

In preparing the unique interpolyesters of this invention bibenzoicacid, or a diester or acid chloride thereof, is reacted with thealiphatic dicarboxylic acid described above, or a diester or acidchloride thereof, and one of glycols described above. An esterinterchange reaction is generally preferred, since the time required toform the interpolyesters of this invention is generally considerablyless, and/ or side reactions can generally be minimized to a greaterdegree than when the free dicarboxylic acids are employed.

The ester interchange method for preparing the interpolyesters of thisinvention proceeds in three stages:

1. One mole of a mixture of a diester of bibenzoic acid Patented Nov.14, 1961 under a variety of conditions. The advantages of and a diesterof one of the saturated aliphatic dicarboxylic acids described above isreacted in the presence of heat and an ester interchange catalyst withat least two moles of a glycol and a monohydric alcohol is distilled offII. The temperature is gradually raised to bring about polymerizationand excess glycol is distilled off; and

III. Polymerization is driven to completion by gradually reducing thepressure to remove the last traces of glycol.

The overall process is illustrated by the following equations:

0 II II (n-DHOYOH wherein Y is a bivalent hydrocarbon or heterohydrocarbon radical as described in (a) through (2) above; R and R aresame or different hydrocarbon radicals derived from a straight orbranched chain aliphatic primary or secondary monohydric alcohol boilingwithin the range from about 64 to 215 C.; R is hydrocarbon residue ofbibenzoic acid and R is the hydrocarbon residue of one of the aliphaticdicarboxylic acids described above.

In a preferred embodiment of this invention, the mixture of monomericdiesters described above (in a ratio of about 40 to 90 mol percent of abibenzoate and about 60 to 10 mol percent of an aliphatic dicarboxylate)and a glycol are weighed into a vessel, the ester interchange catalystadded, and a boiling chip introduced. Stage I ester interchange is thencarried out at atmospheric pressure under nitrogen at a temperaturebetween about 150 and 225 C. (preferably 175 to 200 C.) for about 2 to10 hours, distilling off monohydric alcohol. Polymerization is thenbrought about in stage II by raising the temperature gradually tobetween about 200 and 400 C. (preferably about 260 to 290 C.) over aperiod of about ,6 to 2 hours, continuing polymerization for a period ofabout to 3 hours at this temperature and distilling off excess glycol.In stage III pressure is gradually reduced to below about 5 mm.(preferably 0.2 to 0.5) over a period of about /2 to 4-hours (preferablyabout 1 to 2 hours), followed by continued heating at this elevatedtemperature and reduced pressure for a. period of about 2 to hours. Inthis latter step the last traces of the glycol are distilled off and thereaction mixture becomes progresssively more viscous.

The specific temperatures and heating periods may vary over wider rangesthan those outlined above depending on the observed rate of reaction. Incases where reaction becomes sluggish, higher temperature and/or longerpeiiods of time will be employed. In those cases where the polymer issolidified, or begins to solidify before it is apparent all glycol hasbeen removed, the temperature and/or the heating period are increased.The conditions can be varied considerably depending upon the degree ofthe polyesterification desired, the ultimate properties 4 sought,stability of the polyester being produced and use for which the productis intended. When the desired viscosity is reached under theseconditions in stage III, evacuation and heating are discontinued, aninert gas admitted, the vessel allowed to cool to approximately roomtemperature and the polyester removed. 7

In theory a total of only one mole of one of the glycols is necessary toeffect complete polyesterification with one mole of the mixed monomerdiesters describedherein; however, in practice, it is difficult toattain complete reaction under these conditions. It is therefore usuallynecessary to utilize an excess of the glycol, preferably at least twomoles of glycol to one mole of mixed monomer diesters. Quantitiessubstantially larger than about 2 moles of the glycol may be used;however, since they are not necessary, in the interests of economy, theyare not recommended.

Examples of some of the various monomeric diesters heptanol-l,2-ethyl-hexanol-1, octanol-l, nonanol-l, 2.6-,

dimethyl-3 -methylol-heptane. Diesters derived from these same acids andsecondary monohydric alcohols can be utilized also, e.g. propanol-Z,butanol-2, Z-methyl-butanol-3, pentanol-Z, pen-tanol-3,2-methyl-pentanol-3, 3- methyl-pentanol-2, .hexanol-Z,2,2-dimethyl-butanol-3, 2- methyl-hexanol-3, heptanol-4, octanol-Z,decanol-4.

Since in the preferred process, the alcohols from which the diesters arederived are removed from the reaction zone by boiling, it is generallynecessary to utilize a gly' col having a boiling point higher than thatof the alcohol being evolved. Examples of some of the glycols describedin (a) through (e) above are as follows:

(a) Diethylene glycol, triethylene glycol, tetraethylene glycol,dipropylene glycol, 4,4-dihydroxy-dibutyl ether, other polyoxyalkyleneglycols having 1 to 6 oxyalkylene units wherein said oxyalkylene unitcontains 1 to 10 carbon atoms, 2,2-sulfonyl-diethanol,4,4'-sulfonyl-dibutanol,

3,3 [sulfonyl-bis-( 3-propyl-sulfonyl) ]-dipropanol,

4,4-[-1,4-butylene-disulfonyl-bis-(4-butyl-sulfonyl) ]-dibutanol,

sulfonyl-bis 4-butyl-sulfonyl-4-buty'l-sulfonyl-4-butanol) 6,6'-( 1,6-hcxylene-disulfonyl) -dihexanol,

sulfonyl-bis-[3-(2,2-dimethyl) propanol],

1,3 (2,2-dimethyl propylene-distilfonyl-bis- [3-(2,2-dimethyl)-propyl-sulfonyl-3-(2,2-dimethyl)-propanol],

sulfonyl-bis-[4-(2,2,3,3-tetramethyl)-butanol], etc.,

(b) p-Xylylene glycql, 3,6-bis- (hydroxymethyl -durene,4,4'-bis-(hydroxymethyl -biphenyl, 2,6-bis- (hydroxymethyl -naphthalene, l,5-bis-(-y-hydroxypropyl)-naphthalene,1,4-bis-(fl-hydroxyethyl)-benzene, 1,4-bis- 'y-hydroxypropyl) -benzene,3,6-bis-(fi-hydroxyethyl)-durene, etc.

(c) 2,2'-p-phenylene-dioxy) -diethanol,3,3-(p-xylylene-dioxy)-dipropanol,4,4-(p-phenylene-disulfonyl)-dibutanol,6,6-(p-xylylene-disulfonyl)-dihexanol,2,2-(4,4'-biphenylene-dioxy)-diethanol,

( 1,5 -naphthalene-disulfonyl) -dimethanol,

2,2- [p-phenylene-dioxy-bis- (2-ethoxy-2-cth0Xy) l-diethanol,

2,2-[p-phenylene disulfonyl-bis-(2-ethyl-su1fonyl)1diethanol, etc.

(d) l,4-cyclohexane-p,p'-diethanol, 1,4-cyclohexane-6,6'-dibutanol,

the dihydric alcohol derived from a-pinene having the formula:

CH: CH:

etc.; I

(e) 1,bcyclohexane-dioxy-AH-diethanol,1,4-cyclohexane-disulfonyl-p,p'-diethanol,1,4-cyclohexane-p,p-diethoxy-fl,p'-diethanol, 1,4-cyclohexane-bis-('y-propoxy-y-propoxy-q-propanol) CE: HOCHrCHrO-CHz-C/CH-CH:-CHr-OCHa-CH1OH OH: HOCHz-CHx-SOg-CHz-C CH-CHg-CHrSOrCHrCHgOH CCH:

etc. 3

Examples of some of the aliphatic dicarboxylic acids suitable for thepurposes of this invention include malonic, succinic, glutaric, adipic,pimelic, suberic, azelaic, undecandioic (1,9-nonane-dicarboxylic acid),dodecandioic (1,10-decane-dicarboxylic acid), methyl-malonic,dimethyl-malonic, diethyl -malonic, a-rnethyl succinic,or,a'-dimethyl-succinic, tetramethyl-succinic, mil-dimethyl glutaric,a,a,a',o.'-tetramethyl adipic, p,p,p',fi'-tetramethyl adipic, etc.

The properties of films, fibers, or other molded objects whichconstitute a preferred embodiment of this invention vary greatlydepending in a large measure upon the identity of the glycol utilized toform the interpolyester. Thus melting points, degree of crystallinity,rate of crystallizing, etc. will vary considerably. Interpolyestersformed from difierent glycols within any one of the groups (a) andthrough (e) above will generally be substantially similar to one anotherin their properties. On the other hand, those formed from differentglycols chosen from different groups may vary greatly in theirproperties. In a like manner, the quantity and, to a lesser degree, theidentity of the acid described above in (2) can cause substantialvariation in the properties of the interpolyesters of this invention.Accordingly, although the use of bibenzoic acid in a quantity in therange of 40 to 90 mol percent is generally satisfactory, a range of 50to 80 mol percent is generally preferred where formation of films orfibers is contemplated.

The catalytic condensing agents or ester-interchange catalyst which maybe employed are conventional ones and include, for example, the alkalimetals, the alkaline earth metals; the oxides, carbonates, and boratesof these two groups of metals, the one to six carbon alkoxides of thesetwo groups of metals; magnesium, zinc, and manganese; the oxides ofthese metals; zinc borate; the sulfates, phosphates and acetates ofzinc, cadmium, magnesium aluminum and copper; litharge or a combinationof litharge with antimony trioxide and triphenyl phosphite as describedin US. Patent No. 2,650,213; compounds of the formula:

wherein M is an alkali metal, e.g. lithium, sodium, or potassium, and Ris an alkyl radical containing from 1 to 6 carbon atoms; R can bederived from a lower aliphatic alcohol such as methyl, ethyl, propyl,n-butyl, isobutyl, n-amyl, etc., as described in US. 2,720,506; acomposition consisting of lithium hydride and a glycolsoluble organicsalt of cadmium, magnesium, or zinc as described in US. Patent No.2,681,360.

From about 0.005% to about 0.2% of such catalysts based on the weight ofdiester monomer being condensed may be employed. Higher or lowerpercentages may be employed. Generally, from about 0.01% to about 0.05%of the catalytic condensing agent can be advantageously employed, basedon the weight of dibasic acid diester being condensed. As will beapparent to those skilled in the art, it is generally advantageous froma cost standpoint to utilize the minimum quantity of one of the abovecatalysts which effect optimum results. Obviously, however, quantitieslarger or'smaller than those outlined above will be employed by thoseskilled in the art where needed, e.g. to accelerate or decelerate rateof reaction, to modify propentiesluster, molecular weight, tenacity,etc.

The reaction can be carried out in the presence or absence of a solvent,preferably the latter. Illustrative of such solvents are inert highboiling compounds, such as diphenyl ether, diphenyl, mixed tolylsulfones, chlorinated naphthalene, chlorinated diphenyl, dimethylsulfolane, .etc.

It is essential to exclude oxygen and moisture at all stages of thecondensation reaction. Otherwise discoloration, low molecular weight,and/or insolubilization of the polyester results. Inert atmosphereswhich can advantageously be employed include nitrogen, hydrogen, helium,etc. The exclusion of moisture is readily effected by employingsubstantially anhydrous reactants.

The interpolyesters of this invention can be formed into filaments orfilms by conventional melt extrusion procedures. For example, theinterpolyesters can be melt extruded vertically at a melt temperature ofapproximately 250 C. above the melting point of the interpolyesterfollowed by immediate quenching and orientating.

The following examples are not given by way of limitation, the scope ofthe invention being determined by the appended claims.

EXAMPLE 1 Polyxylylene bibenzoate/sebacate, /20 mol percent Apolymerization vessel fitted with an exit tube, water cooled condenserand water cooled receiver was charged with 14.32 grams (0.048 mole)diethyl bibenzoate, 3.10 grams (0.012 mole) diethyl sebacate and 18.24g. (0.132 mole) p-xylylene glycol. To this mixture were added 0.01 g.zinc acetate, 0.01 g. manganous acetate and 0.005 g. lithium hydride asa mixed catalyst for ester interchange and a boiling chip to preventbumping during subsequent heating. The polymerization vessel wasevacuated and flushed with oxygen-free nitrogen four times prior toheating, then heated rapidly to C. during which time the reactantsmelted with rapid evolution of ethanol. The initial ester interchange toproduce the mixed glycol esters was carried out at 190 C. for four hoursto assure complete conversion to the desired products resulting in thinmobile clear liquids which on cooling solidified to opaque pasty solids.The vessel was gradually heated to 280 C. over a one hour period. Thepolymerization temperature was maintained at 280 C. while the pressurewas gradually reduced over a one hour period to less than 1 mm. andpolymerization continued under these conditions for an additional sixhours. The polymer thus produced was a tan colored liquid whichcrystallized to a .tan opaque solid on cooling, having a birefringentmelting point of 240 C.

EXAMPLE 2 Polyxylylene bibenzoate/succinate, 60/40 mol percent Apolymerization vessel fitted with an exit tube, water cooled condenserand a water cooled receiver was charged with 10.74 grams (0.036 mole)diethyl bibenzoate, 4.18 grams (0.024 mole) diethyl succinate and 18.24g. (0.132 mole) p-xylylene glycol. To this mixture were added 0.01 g.zinc acetate, 0.01 g. manganous acetate and 0.005 g. lithium hydride asa mixed catalyst for ester interchange 7 and a boiling chip to preventbumping during subsequent heating. The polymerization vessel wasevacuated and flushed with oxygen-free nitrogen four times prior. toheating, then heated rapidly to 180 C. during which time the reactantsmelted with rapid evolution of ethanol. The initial ester interchange toproduce the mixed glycol esters was carried outat 180 C. for four hoursto assure com- 7 plete conversion to the desired products resulting inthin mobile clear liquids which on cooling solidified to pasty solids.The vessel was gradually heated to 260 C. over a one hour period. Thepolymerization temperature was maintained at 260 C. while the pressurewas gradually reduced over a one hour period to less than 1 mm. andpolymerization continued under these conditions for an additional sixhours. The polymer thus produced was a yellow colored liquid whichcrystallized to -a yellow opaque solid on cooling, having a birefringentmelting point of 230 C.

EXAMPLE 3 A polymerization vessel fitted with an exit tube, water cooledcondenser and a water cooled receiver was charged with 11.72 gramsbibenzoyl chloride, 4.3 grams sebacyl chloride and 8.29 g. p-xylyleneglycol. To this mixture were added 20 ml. of dioxane as a solvent. Thepolymerization vessel was flushed with oxygen-free nitrogen and heatedto reflux temperature for 6 hours with evolution of hydrogen chloride.The resulting slurry was diluted with 200 ml. of dioxane and filtered toremove precipitated polymer. The latter was washed with acetone anddried at 110 C. The polymer thus produced was a fine white powder with abirefringent melting point of 225 C.

EXAMPLE 4 A polymerization vessel fitted with an exit tube, water cooledcondenser and a water cooled receiver was charged with 11.72 gramsbibenzoy-l chloride, 4.3 grams sebacyl chloride and 6.97 g.cis-1,4-q-uinitol. To this mixture were added 20 ml. of dioxane as asolvent. The polymerization vessel was flushed with oxygen-free nitrogenand heated to reflux temperature for 5.5 hours with stirring resultingin evolution of hydrogen chloride. The resulting slurry was diluted with200 ml. of dioxane and the precipitated polymer isolated by filtration,the polymer was washed with acetone and dried at 110 C. The polymer thusproduced was a fine white powder with a birefringent melting point ofabout 250 C.

EXAMPLE 5 A polymerization vessel fitted with an exit tube, water cooledcondenser and -a water cooled receiver was charged with 14.32 gramsdiethyl bibenzoate, 3.10 grams diethyl sebacate and 14.0 g. diethyleneglycol. To this mixture were added 0.01 g. zinc acetate, 0.01 g.manganous acetate and 0.005 g. lithium hydride as a mixed catalyst forester interchange and a boiling chip to prevent bumping duringsubsequent heating. The polymerization vessel was evacuated and flushedwith oxygen-free nitrogen 3 times prior to heating, then heated rapidlyto 190 C. during which time the reactants melted with rapid evolution ofethanol. The initial ester interchange to produce the mixed glycolesters was carried out at 190 C. for 4 hours to assure completeconversion to the desired products resulting in thin mobile clearliquids which on cooling solidified to white opaque pasty solids. Thevessel was gradually heated to 260 C. over a 1 hour period. Thepolymerization temperature was maintained at 260 C. while the pressurewas gradually reduced over a 1 hour period to less than 1 mm. andpolymerization continued under these conditions for an additional 4.5hours. The polymer th-us produced was a viscous straw colored liquidwhich crystallized to a bufi opaque solid on cooling. The polymer had abirefringent melting point of 125 C. and formed fibers and transparentflexible films.

8 EXAMPLE 6 A polymerization vessel fitted with an exit tube, watercooled condenser and a water cooled receiver is charged with 12.56 gramsbibenzoyl chloride, 3.59 grams sebacyl chloride and 11.88 g.2,2-(p-pheny-lenedioxy)-diethanol. To this mixture is added 20 ml. ofdry o-dichlorobenzene as a solvent. The polymerization vessel is flushedwith oxygen-free nitrogen and is heated to C. for 5 hours with evolutionof hydrogen chloride. The solvent is removed by distillation and thepolymer is heated for an additional two hours at 270 C. The crystallinetan polymer can be formed into fibers and films.

Although illustrated in the preferred embodiment as a batch process, theinterpolyesters of this invention can be produced by continuous methodsalso; for example, the required amounts of the several reactants andcatalyst can be continuously metered into the reaction vessel,maintained therein for the required reaction time under the requiredreaction conditions of temperature and prssure and then continuouslydrawn 0E.

In some instances, it is not practicable to utilize the esterinterchange method described above to prepare the interpolyesters ofthis invention. Accordingly, another preferred embodiment in the presentinvention involves the reaction of a mixture of diacid chlorides and aglycol. According to this embodiment, interpolyesters are prepared bymixing substantially molecular equivalent quantities of the glycol andthe two dibasic acid chlorides. In some cases, it is preferred to addthe glycol to the mixture of dibasic acid chlorides in successiveportions at a rate such that there is no appreciable accumulation ofunreacted glycol. However, it is generally sufiicient to merely mix thethree reactants in a single step. If one or the other of the reactantsis a solid at room temperature, it may be necessary to warm the mixtureor to use a solvent in order to bring about complete solution of thereactants. The working examples herein, it will be noted, utilize bothof these expedients, since the use of a solvent and an elevatedtemperature is the preferred mode of operation. In this initial step, ifan elevated temperature is utilized, it is generally only necessary toheat to a reflux temperature.

During this initial step, rapid and copious e'olution of hydrogenchloride takes place and is usually accompanied by a spontaneous rise intemperature. After the bulk of the hydrogen chloride has evolved, themixture is then warmed gradually to a temperature inexcess of about 200C. accompanied generally by removal of the solvent by distillation. Attimes, it is preferable to utilize reduced pressure, i.e., below about 5mm. of mercury, in

conjunction with the second heating step in order to afiect adequatepolymerization to produce satisfactory molecular weights.

It is necessary in the diacid chloride method of preparing theinterpolyesters of this invention to guard against there being anysubstantial excess of glycol in the final product. In a preferredembodiment, it is generally desirable for the polymer to possess amolecular weight of 10,000 or greater. Accordingly, it is generallynecessary to prevent the inclusion of more than about a one percentexcess of glycol in the finished product. On the other hand, it issometimes possible to produce some of the interpolyesters of thisinvention wherein the final product may contain as much as a 2 /z%excess over the molecular equivalent amount. This does not meannecessarily that the glycol in the reactants as charged should notexceed either of these limitations (i.e. either 1% or 2%% excess), forit has been observed that at times, small amounts of the glycol may belost by volatilization, entrapment, etc. Thus, simply by observation,the optimum quantity to be charged can be determined from the optimumquantities found in the finished product.

We claim:

1. A fil ment and film forming linear interpolyester melting above 140C. of components consisting essentially of a mixture of dicarboxylicacids and at least two mols per mol of mixed acids of a glycol havingthe general formula and --(CH ),,R"(CH wherein R is an aliphatichydrocarbon radical containing 2 to 10 carbon atoms, n is an integer offrom 1 to 6, n' is an integer of from 1 to 2, Ar is from the groupconsisting of monoand di-nuclear arylene radicals containing 6 to 12carbon atoms, m is an integer of from 1 to 4, p andp are integers offrom to 2 and R" is a saturated alicyclic hydrocarbon radical containing6 carbon atoms; said mixture of dicarboxylic acids consistingessentially of from 40 to 90 mol percent of p,p-bibenzoic acid and from60 to 10 mol percent of an aliphatic dicarboxylic acid having thegeneral formula wherein R is a bivalent saturated aliphatic hydrocarbonradical containing 1 to 12 carbon atoms.

2. The filament and film forming linear interpolyester of claim 1wherein the mixture of dicarboxylic acids consists essentially of from50 to 80 mol percent of p,p'- bibenzoic acid and from 50 to 20 molpercent of the aliphatic dicarboxylic acid.

3. Process of preparing filament and film forming linear interpolyestersmelting above 140 C. which comprises reacting the components consistingessentially of a mixture of from 40 to 90 mol percent of a lower alkyldiester of p,p'-bibenzoic acid and from 60 to 10 mol percent of a loweralkyl diester of an acid having the following general formula:

wherein R is a bivalent saturated aliphatic hydrocarbon radical havingfrom 1 to 12 carbon atoms, and a glycol having the general formulawherein Z is a radical selected from the group consisting of )n 2)m 2)ma and (CH,),R"(CH wherein R is an aliphatic hydrocarbon radicalcontaining 2 to 10 carbon atoms, n is an integer of from 1 to 6, n is aninteger of from 1 to 2, Ar is from the group consisting of monoanddi-nuclear arylene radicals containing 6 to 12 carbon atoms, m is aninteger of from 1 to 4, p and p' are integers of from 0 to 2 and R is asaturated alicyclic hydrocarbon radical containing 6 carbon atoms; saidreaction taking place at a temperature above C. in the presence of anester interchange catalyst and in the ab scnce of oxygen and moisture.

4. The process of claim 3 wherein the initial reaction temperature iskept from 150 to 225 C. until no further alcohol is liberated andthereafter the temperature is raised to from 200 to 400 C. with agradual reduction of reaction pressure to less than 5 mm. of mercury.

5. The process of claim 4 wherein the initial temperature ranges from to200 C., the temperature is raised to from 260 to 290 C. and the pressureis reduced to from 0.2 to 0.5 mm. of mercury.

References Cited in the file of this patent UNITED STATES PATENTSCaldwell et al Dec. 20, 1955 Fisher Sept. 11, 1956 OTHER REFERENCESRothrock et al Mar. 2', 1948

1. A FILAMENT AND FLIM FORMING LINEAR INTERPOLYESTER MELTING ABOVE140*C. OF COMPONENTS CONSISTING ESSENTIALLY OF A MIXTURE OF DICARBOXYLICACIDS AND AT LEAST TWO MOLS PER MOL OF MIXED ACIDS OF A GLYCOL HAVINGTHE GENERAL FORMULA